Apparatus for hardening hack-saw blades and the like



Jan. .22, 1935. A. H. EVANS ET AL APPARATUS FOR HARDENING HACK SAWBLADES AND THE LIKE 2 Sheets-Sheet l Filed March 3, 1932 Jan. 22, 1935.A, H, EVANSET AL 1,988,869

APPARATUS FOR HARDENING HACK SAW BLADES AND THE LIKE Filed March 3, 19322 Sheets-Sheet 2 er f/ LN e' ff s I 5 i@ ,d y? a@ @VTV-"TV Patented Jan.2K2, 1935 Y UNlTED STATES PATENT OFfFlfCflE'.

.APPARATUS :FOR :HARDENING lHACK-'SKW BLADES AND THE vLIKEAlexanderHavelockEvans, Cheadle, and Charles Norman Fletchen'Cheadle-Hulme, England "7 Claims. n (Gl. 21S- 11) .invention ,relatesto an improved method 'of :and means Afor fhardening :hack-saw zblades,4and exclusively Lto 'hack-saw blades of. high` speed steel.

The .hardeningof :high speed steel saw blades .by heat treatment hasbeen .practiced f'or many 1years and is known Ato .present :certainproblems. Firstly, there is 4the characteristics of the ymetal vitselfrequiring very high temperatures. :Secondly, :thereis the natureof the.article itself -and the questionfof :burning or distortion during .boththe heatingand cooling,.-and Lthirdly, Ithere lis .the question .of.subsequent annealing `or fletting :down:of theends.ofthesawtorgive'them temper and reduce their .brittleness or`liabilityzto .fracture in thelclamps when in use.

The :usual lprocess ffor 'hardening `high :speed steel `:hack-saw.:blades yconsists a of hardening the whole i saw blade .and subsequentlyannealing :the ends in a separate process. It-.is welbknoWnLthat fhigh`percentage tungstensteels,A and like high- 'speed steels, .are very.difficult to :anneal fatter 'hardening f' and can i only ybew,thoroughly annealed fbyza :prolonged iheat :treatment The `cost ofannealing .the ends of :highe'speed 'steel ,saw :blades may ,well exceedthe :cost :of the :hardening sand even '..then 'the degree anduniformity :of -the annealing is generally tuncertain. 4Also the@heating of high-speedisteel saw..b1ades for .their harden- .ingis quiteeaproblem owing tto the highztemperfaturesrequired.Knownrapparatusapplicable for this f purpcse gare, chamber 'furnacesheated fby gas, oil, .or lelectricity ,using :either .radiated :heat or.conducted heat 4by sal ,or rother fmedia, all lof which `apparatus in`practice involve yheavy ,maintenance costs =.due to the Ynecewary .high

working temperatures. ;Further,-;the 4sizepofzblade :which .can :beheated in ya furnace is .limited iby `the length or depthoftheurnace,andthegreat- .er this dimension, .the more .difficult '.it to f ob-'.tain Vand maintain :the necessary .temperature throughout, l.with:suicient iaccuracy. [didiculty :is Yconsiderably increasedunder-.working conditions .With the .loading and zlmloadingfofthe.urnaca @especially Las :the loading .is :performed .with `.a;coo1 fchargetending to cause .uneven tem- .p eratures I,and .cooling fof thefurnace .Itis :also almown factginfheating any;y articlefintaziurnace,.all fedges and projections .fare :liable ;,to 'beovervheated-Landtsomepofitheredge*islost. v

Such .blades Leven Athough 1 made -.of :high speed :and vnormally A.airhardening steel are fat :present usually hardened by quenching. The:quenching is done irrespective fof the -kind L of lsteelgimmediatelythe blades are-drawn fromthe furnacato 4prevent the :twisting andywarping which otherwise rapidlytake place, 'the .bladesbeingxusually:held lunrestrained` `It'has however, beenproposed,infthelheat treatmentof .steel rails, rods, Wire vtubes and -even saws of carbon steel'butknothigh speed steel vto employ a. heavy electric :current passedthrough ,the yarticle rfor heating it, and except iin the i case ofthesaws tosuspend the same to keep ithem straightrandalso to hold themso ,as to permit expansion during heating.

'In the use of an electric currentforheating an article it is `a -knowndrawback that the end pieces, to Whichthe electrodes are Vconnected,.do

Inctz'get rthe same zheating. 'This drawback has usuallybeenfdealt'withby treating suchendsas 'scrap,.and,infone case afspecialform of electrode .hasjbeen evolved toget uniform'heating forsits :fulllength. :In no case :has itbeen previously :proposed to make useof thiseffect at the ends.

According :to `:the invention lthe improved process of lhardeningphigh`speed steelfhaokgsaw blades -wherein .an velectric current is :passedthrough the blade supplied 'through clamps lholdingthe ends o'f'theblade characterized1in:that f .the clamps are 'of Aa-sizettocover-the Ventire end :parts :of uthe blade and of a:relatively large:mass

so that such .ends-zofl-the, s`aw;blade. are L-keptrrelativelyy coldtojpreventthemxattaining -ahardening temperature.

:In the accompanying 'drawings-- fFig. lzis-,affront felevationioi oneexample Aof apparatusfor hardening hack-saw-bladesin accordance ywiththe invention.

Figi-2V is a side elevation -of Eig e1.

lFigs. 3 ande are plan z-andside'elevationito alarger'scale "ofAtheclamps-for thersawblades.

As illustrated the; apparatus :consists of: a: stand :a Aabout .7 Ffeethigh supporting -a 'vertical slate lpanelibimeasuring 4 fx 4thelowerfedge vofnwhioh panel 1is about 2' 'from the floor. l,Qn itheifront face of the panel b are two vertical electrically conductive:slide rails c. oftbronza: graduatediat c1 totake the-.variouslengthsfofzolade. vSliding .ver-

'ticallyonlthese lslidesrailszis afcrosssmemberid f" to Jwhich areattached-three.-quick-acting. clamps e,.one yof Whichis describedlaterlindetall, gripping the top ends of thebladeif. The crossmem berdsuspendedbycablesidlfpassing over pui leys 5d on the :.shaftd #mounted`vin brackets sethe cables being connected to a counter weight d4. Theslide rails c are joined at the top by a bus bar c2 to which isconnected the main conductor c3. The above assembly is of sufficientcross sectional area to carry the necessary heavy current up to 10,000amperes, without undue heating. Alternating current of the usual lowfrequency (about 50 cycles) is preferred for the process. Attached tothe bottom end of the panel b there are three cast iron vertical slidesg, two of which are shown ntted with a separate bronze sliding carriageg1 to the upper ends of which are fitted quick-acting clamps h for thebottom ends of the blades, similar in detail to the upper quick-actingclamps e. The upper end of the slideis provided with a stop g2. To theother and lower end of the slides g there is fitted a flexible laminatedcopper conductor i leading to bottom terminals 7 which are separated onefrom the other. Below these bottom terminals is a slide rail-lc fittedwith a sliding terminal or shoe k1 which can be moved into contact witheach of the above separate three terminals y enabling the operator tomake or break the circuit on each or either of the blades f securedbetween the upper and lower clamps e and h. The sliding carriage g1 atthe bottom of the slate panel, are each provided with a suitablecounter-balancing arrangement consisting of weights g3 attached tostraps g4 and suspended over pulleys g5 carried by the slides g wherebythe tension can be adjusted as required for blades of the variouscross-sections can be suitably arranged. The movement of thiscounter-balancing arrangement can be conveniently used for indicatingthe various temperatures necessary for the production of the saw blades.For that purpose a pointer Z is provided connected to one of the pulleysg5 besides each of which is arranged a shield Z1. 'I'he pulley carryingthe pointer is pinned to its cable so that the pointer moves definitelywith the carriage g1. An index Z2 may be provided adapted to clamp tothe edge of the shield and to be used as a mark in co-operation with thepointer. The electric circuit is controlled by a contactor, which iscontrolled by Va relay button switch n or which may be automaticallyoperated from the movements of the sliding carriage g directly, or bycontacts operated by the pointer to switch 01T when the predeterminedtemperature has been reached. The sliding contactor shoe k1 is tted witha flexible laminated conductor k2 for the return circuit.

The clamps each consist of a body having a V- shaped opening, thevertical face 'o o-f which forms one of a jaw. The other' face of theopening is inclined forward at about 45 degrees, and shaped to form aslide for a sliding jaw block p having a vertical face p1 opposite tothe face o. The body of the clamp is tted with a projecting `stud qsecured into the bottom of the V-shaped opening and parallel with theinclined face thereof which stud passes through the sliding jaw block pand is provided with a spring q1 and adjustable nuts q2 for leading thespring, forcing the sliding jaw down its inclined slide into theV`shaped opening. f

On each side of the sliding jaw is a lug p2 which lugs are adapted to beengaged by the cam shaped ends r of a lever r1 pivoted at r2 on the bodyof the clamp, such engagement operating to move back the sliding jaw pagainst the spring q1. The pressure or grip of the jaw is dependent uponthe springY q1 the leading of which is adjustable as aforesaid by thenuts q2. The upper and` lower clamps are of identical construction butare reversed in position, the bodies of the upper clamps being securedto the cross member d and the bodies of the lower clamps being eachsecured to their separate carriages g1.

For moving the sliding shoe k1 into engagement with the terminals y ahand wheel s is provided on the side of the frame ma convenient positionadjacent to the control switch n. The shoe k1 is secured toa chain s1arranged below the rail lc on pulleys s2 one of which is connected by afurther chain s3 to the hand wheel s.

In operation, for hardening high speed steel blades the machine is rstset by raising or lowering the cross member d to the graduation on theslide rails c for the length of blade to be hardened. The electricalapparatus which is not described as its construction forms no part ofthis invention, is then set to give the required voltage and amperagefor that section and length of blade. Each blade is then ttedseparately, rst into the upper clamp by raising the lever r1 insertingthe blade into the open clamp, and then lowering the lever allowing theclamp to close. The carriage g1 carrying the lower clamp is then raisedwith the clamp open until it comes against the stop g2 and the clamp isthen closed on the saw blade when the required length of each end of thesaw, to be kept soft, will be within the clamps. The saw will then beunder slight tension due to the. unbalanced weight of the carriage g1,which must only be a few ounces but sumcient so that the carriage willdescend with the expansion of the saw blade as the latter expands onheating.

The sliding shoe k1 is then moved along its rail 1c by means of the handwheel s until it is below and in engagement with the terminal :i of thelower clamp toy which the saw blade has just been tted. The electriccurrent is then switched on by pressing the lon control button of therelay switch n. The current heats the blade to the required temperaturein about 10 to seconds, and as the blade extends the carriage g1descends keeping the blade under a slight tension. The descent of thecarriage is indicated by the movement of the pointer Z in front of theshield Z1 and when the pointer is seen to have reached the index Z2 thecurrent is switched off by pressing the off" button of the switch n. Thesliding shoe icl may then be moved on to the next terminal y and theheating up of another blade started while the other blade is cooling inthe clamps and still under slight tension. The index Z2 is set for theblades in the rst place by the. aid of a pyrometer, such as that knownlas the disappearing filament` pyrometer. A @further saw blade may befitted in the adjacent clamps while one is being heated without risk tothe operator. By the time the second blade has been heated and the shoemoved across for heating the third blade, the rst blade will have cooledenough to be removed without distortion and will be air hardened. 'Iheheating up of the saw must extend over a certain period of time to allowthe heat to extend to the teeth which heat up more slowly than the bodyof the saw. This lag or delay in the heating up of the teeth is indirect contra distinction to the advanced heating up or overheating ofthe teeth when the blade is heated in a furnace. I'he consequentadvantage of this difference is' that the blade may be taken to highertemperatures without danger of fusing and with much less deteriorationof the edge of the teeth.

Cooling may be assisted by air blast or means may be provided forquenching (which is necessary for carbon or low percentage tungstensteel blades) either with or without removal of the blade from thegrips.

The apparatus may be designed for a continuous process, the grips beingmounted on conveyors and the blades carried automatically through theheating and cooling stages of the hardening process. A rotating drum orcarriage may be used instead of the conveyors. The design of such anapparatus -might include the automatic feed of the blades to the clampsand their delivery after treatment and is not described or claimedtherein except in so far as it embodies this envention as it is withinthe capacity of any engineer to evolve a design of such apparatus.

The invention is not limited to the particular details of the aboveapparatus, the important features of the invention being the singleprocess of hardening the saw and at the same time providing therelatively softer ends thereof, the high thermal efficiency of thedirect heating, the economy of the blade acting as its own heatingelement, the prevention of distortion, the ease of temperature control,the simplicity oi' operation and the almost complete elimination ofscrap during heat treatment from burning or damaging of the teeth, orfrom other reasons.

What we claim is:-

l. Apparatus for use in the hardening of high speed steel hack-sawblades by passing a heavy current of electricity through them,comprising a vertical frame or back with a vertical slide rail cn oneface, a clamp slidable on such rail to hold the upper end of a sawblade, counterbalancing means for the clamp passing over a pulley at thetop of the frame, means for setting the clamp in an adjusted position onthe rail, a further clamp mounted in a vertical slide at a lower part ofthe irai-ne to hold the lower end of the saw blade, a stop to limit theupward movement of such further clamp, a counterbalance weight for thefurther clamp but of slightly less weight than the clamp, means forinsulating the two clamps from each other cn the frame or back, andmeans for connecting the clamps to a current supply, the clamps being ofa size to cover substantially the entire end parte of the blade andbeing of a relatively large mass so as to keep the ends of the bladesrelatively cool and soft.

2. Apparatus for use in the hardening of high speed steel hack-sawblades by passing a heavy current of electricity through them,comprising a slab of non-conducting material supported vertically in aframe, vertical slide rails thereon and a common clamp-carrying bar onthe slide rails, clamps mounted in an inverted position o-n the carryingbar for receiving the upper ends of saw blades, a counter-balance weightfor the clamp-carrying bar connected thereto by rflexible elementspassing over pulleys at the top of the frame, further vertical sliderails on the slab, at its lower part, a clamp slidable on each of thefurther rails to receive the lower end of a saw blade, stops to limitthe upward movement of the lower clamps, a counter-balance weight foreach lower clamp but of slightly less weight, and means for connectingthe clamp-carrying bar and the lower clamps to an electric currentsupply circuit, the clamps being of a size to cover substantially theentire end parts of the blade and being of a relatively large mass so asto keep the ends of the blades relatively cool and soft.

3. Apparatus as claimed in claim 2, wherein the means for connecting thelower clamps to the electric circuit comprises a contact member mountedon a conveyor extending across the frame, and means for traversing thecontact below the said clamps to engage any one of them at will.

4. Apparatus as claimed in claim 2, wherein the means for connecting thelower clamp to the electric circuit comprises a laminated copperconductor of U-shape below and connected to each such clamp, a terminalblock on the lower arm of each conductor, and a contact member mountedon a conveyor extending across the frame with means to traverse thecontact member into engagement with any one of the terminal blocks.

5. In apparatus as claimed in claim l, a pointer operated by relativemovements of the lower clamp and its balance weight to indicatevariations in the length of the saw blade.

6. In apparatus for hardening of high speed steel hack saw blades bypassing a heavy current of electricity through them, a clamp for eachend of the saw blades comprising a fixed jaw, a movable jaw mounted onthe fixed jaw and slidable in a direction at an acute angle to thecontacting jaw faces, a compression spring tending always to close theclamp, and a hand lever pivotedly mounted on the fixed jaw with a camextension to engage and move the slidable jaw into the open positionagainst the resistance of the spring, the clamp jaws being of a size tocover substantially the entire end parts of the blade and being of arelatively large mass so as to keep the ends of the blades relativelycool and soft.

7. Apparatus for use in the hardening of high speed steel hack sawblades by passing a heavy current of electricity through them,comprising an upper clamp adjustable to set positions on a verticalframe, a balance weight therefor, a lower clamp slidable vertically onthe frame, a balance Weight therefor of slightly less weight and meansto connect the clamps to opposite poles of an electric circuit, theclamps being of a size to cover substantially the entire end parts cfthe blade and being of a relatively large mass so as to keep the ends ofthe blades relatively cool and soft.

A. H. EVANS.

C. NORMAN FLETCHER.

